Depending on who you listen to, Iran is either an unlikely potential ally of the United States in Afghanistan, with shared common interests in stabilising the country, or a spoiler ready to support its old enemies the Afghan Taliban in order to undermine Washington’s position. Others put it somewhere in between, like every other country in the region biding its time in order to make sense of the U.S. exit strategy from Afghanistan, while also picking its way through a showdown with the United States over its nuclear programme.

Evidence so far of its exact intentions on Afghanistan is sketchy. After initially supporting the United States following the overthrow of the Taliban in 2001 -Shi’ite Iran has no natural sympathy with the hardline Sunni Taliban – it found itself branded by former president George W. Bush as part of the axis of evil in 2002, and then after 2003 squeezed between U.S. troops in both Iraq and Afghanistan.

At the same time, Iran is keen for stability in Afghanistan in part to help clamp down on a booming heroin trade which has left it with its own huge drug addiction problem. Nearly a year ago, it offered help in combating the Afghan drugs trade at a conference in The Hague attended by U.S. Secretary of State Hillary Clinton.

Its police chief was quoted this month by Press TV as saying that, ”in addition to hosting a large domestic consumption market for narcotics, Iran is the shortest drug trafficking route from Afghanistan to the world. Opium-based products such as morphine and heroin are usually transported to European countries and other products such as hashish are trafficked to other countries such as the Persian Gulf littoral countries. Given all of this, naturally Iran is the country suffering here.”

According to the Wall Street Journal, “some analysts argue that Iran and the U.S. actually share the same long-term goal in Afghanistan, which is creation of a stable government. The U.S. needs a stable Afghanistan so al Qaeda and other terrorist groups don’t again form operating bases there. Iran needs a stable border free of refugees and drug trafficking.”

It quotes George Gavrilis, a fellow at the Council on Foreign Relations, as arguing in a paper last year that Iran has, overall, behaved responsibly toward Afghanistan. “Iran works furiously to protect its vast boundary with Afghanistan, responds to unrest in its border provinces with an iron fist, and avoids major intrigues in Kabul,” he wrote. As a result, it quoted him as saying, ”it’s high time for the United States to engage Iran over Afghanistan in a way that is public, decisive, and comprehensive. Strategic cooperation is possible because the United States and Iran have converging interests and common aversions in Afghanistan.”

So will we see cooperation or confrontation between the United States and Iran over Afghanistan? The question is probably impossible to separate from the row over Iran’s nuclear programme. And you also need to keep an eye on the role played by Saudi Arabia, Iran’s main regional rival, which along with being a staunch ally of Pakistan was one of only three countries to recognise the Taliban government when they were in power from 1996 to 2001.